The invention relates broadly to dental materials filled with a non-heavy metal oxide and a heavy metal oxide to provide radiopaque dental materials that can be used as restoratives, adhesives, cements, orthodontic devices, mill blanks and prostheses. More specifically, the invention relates to hardenable dental materials filled with particles of silica and a heavy metal oxide, where the particles impart radiopacity, high strength, and good resistance to abrasion.
Dental materials generally have unique requirements as compared to the broad spectrum of composite materials. For health reasons, dental materials should be suitable for use in the oral environment. In certain instances, strength and durability of a dental material is important to ensure satisfactory performance. For example, in dental work that is performed at dentition locations where mastication forces are generally great, high stength and durability is desirable. In other instances, aesthetic character or quality (e.g., luster and translucency) is highly desired. This is often the case where dental work is performed at locations where a tooth repair or restoration can be seen from a relatively short distance.
Strength in a dental material is typically achieved by adding fillers. Generally, a dental material possessing greater mechanical strength characteristics is filled or loaded with larger sized particles; i.e particles having a diameter greater than about 0.4 micrometers. These materials are often referred to as hybrid composites. A disadvantage to these composites, however, is their tendency to lack luster and aesthetic character. Another disadvantage of composites with large-sized particles is that with repeated toothbrushing (a requirement for oral hygiene), the hardened resin can wear away, exposing the large filler particles and leave a dull, unaesthetic surface. This can subsequently lead to plaque accumulation.
Increasing filler levels can also increase the strength of a dental material. However, this can lead to increased visual opacity, thereby reducing translucency and aesthetic quality.
Canadian Patent Application 2,202,732 teaches polymerizable dental materials comprising a sol of surface modified silica particles in a liquid, organic dispersion agent. The silica particles comprise about 35 wt % of the dental material.
Good rheological properties in unhardened dental materials are advantageous to a dental practitioner. This allows the practitioner to easily manipulate and place the material in its desired location and achieve proper contact and anatomical form before hardening or curing. Nanometer sized (xe2x80x9cnano-sizedxe2x80x9d) silica particles, most often in the form of fumed silica, have been dispersed in polymerizable dental resins. A fumed silica material available from DeGussa, under the trade designation OX-50, has had widespread use. Materials made with fumed silica dispersed at high loading levels within the resins, however, result in dilatant compositions that are generally impractical for dental practice. A well-recognized dental reference book by Craig, entitled, xe2x80x9cRestorative Dental Materials,xe2x80x9d 8th ed., 1989 teaches that highly-loaded fumed silica materials generally provide materials with poor rheological properties. (See e.g., p.256 of Craig.) Thus, conventional materials whose concentrations of an inorganic component (particles) are adjusted for a desired strength, typically result in undesirably dilatant materials.
It has also been the practice to incorporate pre-polymerized particles to overcome the dilatant rheology. These, however, can result in low strength materials.
It is generally desired that the dental material blends well with the surrounding dentition and looks life-like. Aesthetic quality in dental materials is typically achieved by creating material that has tooth-like colors/shades. xe2x80x9cMicrofills,xe2x80x9d a certain class of dental materials, tend to have some luster, to better replicate tooth appearance. One example of a xe2x80x9cmicrofillxe2x80x9d is commercially available under the trade designation SILUX PLUS (3M Co., St. Paul, Minn.). Microfills, however, generally have less mechanical strength than hybrid composites or xe2x80x9cmacrofills.xe2x80x9d Thus, in current practice, for applications where high strength and high aesthetic quality are desired, a practitioner is typically required to first use an underlying foundation of a material possessing high physical strength followed by an overlying layer of a microfill.
Radiopacity of a dental material can be useful in dentistry. Radiopaque materials can be examined using standard dental X-ray equipment, thereby facilitating long term detection of marginal leakage or caries in tooth tissues adjacent to a hardened material. U.S. Pat. No. 4,503,169 describes a radiopaque, low visual opacity (i.e. translucent) dental composite with non-vitreous zirconia-silica microparticles made by a sol-gel process.
The invention provides dental material comprising a hardenable resin, non-heavy metal oxide particles, and a heavy metal oxide. The dental materials have high aesthetic quality, high strength, and good resistance to abrasion.
xe2x80x9cHardenablexe2x80x9d is descriptive of a material that can be cured or solidified e.g., by heating to remove solvent, heating to cause polymerization, chemical crosslinking, radiation-induced polymerization or crosslinking, or the like.
xe2x80x9cNon-heavy metal oxidexe2x80x9d means any oxide of elements other than those of heavy metals.
xe2x80x9cHeavy metal oxidexe2x80x9d means an oxide of metals having an atomic number greater than 28.
In an aspect of the invention, silica particles combined with a heavy metal oxide can provide a strong, radiopaque yet translucent (i.e. low visual opacity) dental material.
In another aspect of the invention, the dental materials of the invention can be used as dental adhesives, artificial crowns, anterior or posterior fillings, casting materials, cavity liners, cements, coating compositions, mill blanks, orthodontic devices, restoratives, prostheses, and sealants.
In a further aspect of the invention, the hardenable resin can be an acrylate, methacrylate, or epoxy or combinations thereof.
In another aspect of the invention, methods of using the materials of the invention comprise placing the material in the oral environment, where the surface or topography is changed prior to or after the placement in the mouth and hardening the material.